A proliferation of portable battery operated electronic devices, e.g., cell phones, personal digital assistants (“PDAs”), electronic book readers, portable games players, MP3 music players, digital cameras, etc., have created a need for external power sources to recharge the batteries thereof. Heretofore, specific use battery chargers that plug into a standard alternating current (“AC”) power wall-mount outlet have been supplied with their respective battery operated electronic device. These battery chargers have been either a step-down transformer with or without AC to direct current (“DC”) rectification, or an electronic step-down voltage switch mode power supply (“SMPS”).
As technology has advanced, more and more devices have been configured to connect with a Universal Serial Bus (“USB”) interface that is capable of supplying both data and power to the portable device. Use of a USB interface eliminates the requirement for separate power and data connectors in the portable device. Problems exist however when a USB battery charger has been misplaced, more than one portable device requires charging, and/or a personal computer is not available as a USB charger. Also some inexpensive USB battery chargers are not energy efficient, e.g., poor power and heat management.